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In
chemistry Chemistry is the scientific Science () is a systematic enterprise that builds and organizes knowledge Knowledge is a familiarity or awareness, of someone or something, such as facts A fact is an occurrence in the real world. T ...

chemistry
, an oxonium ion is any
oxygen Oxygen is the chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the same ...

oxygen
cation An ion () is an atom An atom is the smallest unit of ordinary matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by having volume. All everyday objects that can be touched are u ...
with three bonds. The simplest oxonium ion is the
hydronium In chemistry Chemistry is the scientific Science () is a systematic enterprise that builds and organizes knowledge Knowledge is a familiarity or awareness, of someone or something, such as facts A fact is an occurrence in th ...

hydronium
ion H3O+.


Alkyloxonium

Hydronium is one of a series of oxonium ions with the formula R''n''H3−''n''O+. Oxygen is usually pyramidal with an sp3 hybridization. Those with ''n'' = 1 are called primary oxonium ions, an example being protonated alcohol (e.g.
methanol Methanol, also known as methyl alcohol, amongst other names, is a chemical A chemical substance is a form of matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by having volume. ...

methanol
). In acidic media, the oxonium
functional group In organic chemistry, a functional group is a substituent or moiety (chemistry), moiety in a molecule that causes the molecule's characteristic chemical reactions. The same functional group will undergo the same or similar chemical reactions re ...
produced by protonating an alcohol can be a
leaving group In chemistry Chemistry is the scientific Science () is a systematic enterprise that builds and organizes knowledge Knowledge is a familiarity or awareness, of someone or something, such as facts A fact is an occurrence in the ...
in the
E2 eliminationImage:EliminationReactionCyclohexene.svg, frame, Elimination reaction of cyclohexanol to cyclohexene with sulfuric acid and heat An elimination reaction is a type of organic reaction in which two substituents are removed from a molecule in either a o ...

E2 elimination
reaction. The product is an
alkene In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, behavior and the changes they undergo dur ...

alkene
. Extreme acidity, heat, and dehydrating conditions are usually required. Other hydrocarbon oxonium ions are formed by
protonation In chemistry, protonation (or hydronation) is the adding of a proton A proton is a subatomic particle, symbol or , with a positive electric charge of +1''e'' elementary charge and a mass slightly less than that of a neutron. Protons and neutrons ...
or
alkylation Alkylation is the transfer of an alkyl In organic chemistry, an alkyl substituent is an alkane missing one hydrogen. The term alkyl is intentionally unspecific to include many possible substitutions. An acyclic alkyl has the general formula of ...

alkylation
of
alcohol In chemistry, alcohol is an organic compound that carries at least one hydroxyl functional group (−OH) bound to a Saturated and unsaturated compounds, saturated carbon atom. The term alcohol originally referred to the primary alcohol ethan ...
s or
ether Ethers are a class of organic compound In , organic compounds are generally any s that contain - . Due to carbon's ability to (form chains with other carbon s), millions of organic compounds are known. The study of the properties, reaction ...

ether
s (R−C−−R1R2). Secondary oxonium ions have the formula R2OH+, an example being protonated ethers. Tertiary oxonium ions have the formula R3O+, an example being
trimethyloxonium
trimethyloxonium
. Tertiary
alkyl In organic chemistry Organic chemistry is a branch of chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, pr ...

alkyl
oxonium
salts In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, behavior and the changes they undergo during ...
are useful
alkylating agent Alkylation is the transfer of an alkyl In organic chemistry Organic chemistry is a branch of chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s ...
s. For example,
triethyloxonium tetrafluoroborate Triethyloxonium tetrafluoroborate is the organic Organic may refer to: * Organic, of or relating to an organism, a living entity * Organic, of or relating to an anatomical organ (anatomy), organ Chemistry * Organic matter, matter that has come ...

triethyloxonium tetrafluoroborate
()(), a white crystalline solid, can be used, for example, to produce ethyl esters when the conditions of traditional Fischer
esterification An ester is a chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entity, molecular entities) composed of atoms from more than one chemical element, element held together by chemic ...

esterification
are unsuitable. It is also used for preparation of enol ethers and related functional groups.
Oxatriquinane
Oxatriquinane
and
oxatriquinacene
oxatriquinacene
are unusually stable oxonium ions, first described in 2008. Oxatriquinane does not react with boiling water or with
alcohol In chemistry, alcohol is an organic compound that carries at least one hydroxyl functional group (−OH) bound to a Saturated and unsaturated compounds, saturated carbon atom. The term alcohol originally referred to the primary alcohol ethan ...
s,
thiol A thiol () or thiol derivative is any organosulfur compound Organosulfur compounds are organic compound , CH4; is among the simplest organic compounds. In chemistry Chemistry is the scientific discipline involved with Chemical element, elem ...

thiol
s, halide ions, or
amine In organic chemistry Organic chemistry is a branch of chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, ...

amine
s, although it does react with stronger
nucleophile In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, behavior and the changes they undergo during a ...

nucleophile
s such as
hydroxide Hydroxide is a diatomic anion with chemical formula A chemical formula is a way of presenting information about the chemical proportions of s that constitute a particular or molecule, using symbols, numbers, and sometimes also other sym ...
,
cyanide A cyanide is a chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entity, molecular entities) composed of atoms from more than one chemical element, element held together by che ...

cyanide
, and
azide Azide is the anion An ion () is an atom An atom is the smallest unit of ordinary matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by having volume. All everyday objects tha ...

azide
.


Oxocarbenium ions

Another class of oxonium ions encountered in
organic chemistry Organic chemistry is a branch of chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, behavior and th ...
is the
oxocarbenium An oxocarbenium ion (or oxacarbenium ion) is a chemical species characterized by a central sp2-hybridized carbon, an oxygen substituent, and an overall positive charge that is delocalized between the central carbon and oxygen atoms. A oxocarbenium i ...

oxocarbenium
ions, obtained by
protonation In chemistry, protonation (or hydronation) is the adding of a proton A proton is a subatomic particle, symbol or , with a positive electric charge of +1''e'' elementary charge and a mass slightly less than that of a neutron. Protons and neutrons ...
or
alkylation Alkylation is the transfer of an alkyl In organic chemistry, an alkyl substituent is an alkane missing one hydrogen. The term alkyl is intentionally unspecific to include many possible substitutions. An acyclic alkyl has the general formula of ...

alkylation
of a
carbonyl In organic chemistry Organic chemistry is a branch of chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, pro ...

carbonyl
group e.g. R−C=−R′ which forms a
resonance structure In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound, compounds composed of atoms, molecules and ions: their composition, structure, properties, behavior and the changes they und ...
with the fully-fledged
carbocation A carbocation () is an ion An ion () is an atom An atom is the smallest unit of ordinary matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by having volume. All everyday ...
R−−O−R′ and is therefore especially stable: :


Gold-stabilized species

An unusually stable oxonium species is the gold complex tris riphenylphosphinegold(I)xonium tetrafluoroborate, Ph3PAu)3OBF4], where the intramolecular aurophilicity, aurophilic interactions between the gold atoms are believed responsible for the stabilisation of the cation. This complex is prepared by treatment of Ph3PAuCl with
Ag2O
Ag<sub>2</sub>O
in the presence of NaBF4: :3 Ph3PAuCl + Ag2O + NaBF4Ph3PAu)3Osup>+ F4sup>− + 2 AgCl + NaCl It has been used as a catalyst for the propargyl
Claisen rearrangement The Claisen rearrangement is a powerful carbon–carbon chemical bond, bond-forming chemical reaction discovered by Rainer Ludwig Claisen. The heating of an allyl Vinyl group, vinyl ether will initiate a Sigmatropic reaction, ,3sigmatropic r ...
.


Relevance to natural product chemistry

Complex bicyclic and tricyclic oxonium ions have been proposed as key intermediates in the biosynthesis of a series of
natural product A natural product is a chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entity, molecular entities) composed of atoms from more than one chemical element, element held together b ...
s by the red algae of the genus ''
Laurencia ''Laurencia'' is a genus Genus (plural genera) is a taxonomic rank Taxonomy (general) is the practice and science of classification of things or concepts, including the principles that underlie such classification. The term may also refer t ...

Laurencia
''. Several members of these elusive species have been prepared explicitly by total synthesis, demonstrating the possibility of their existence. The key to their successful generation was the use of a
weakly coordinating anion Anions that interact weakly with cations are termed non-coordinating anions, although a more accurate term is weakly coordinating anion. Non-coordinating anions are useful in studying the reactivity of electrophilic cations. They are commonly found ...
(Krossing's anion, l(pftb)4sup>−, pftb = perfluoro-''tert''-butoxy) as the counteranion. As shown in the example below, this was executed by a transannular halide abstraction strategy through the reaction of the oxonium ion precursor (an
organic halide Halocarbon compounds are chemicals in which one or more carbon atoms are linked by covalent bonds with one or more halogen atoms (fluorine, chlorine, bromine or iodine – ) resulting in the formation of organofluorine compounds, organochlorine ...
) with the silver salt of the Krossing's anion Ag l(pftb)4CH2Cl2, generating the desired oxonium ion with simultaneous precipitation of inorganic
silver halide A silver halide (or silver salt) is one of the chemical compound A chemical compound is a chemical substance A chemical substance is a form of matter In classical physics and general chemistry, matter is any substance that has mass and ...
s. The resulting oxonium ions were characterized comprehensively by
nuclear magnetic resonance spectroscopy Nuclear magnetic resonance spectroscopy, most commonly known as NMR spectroscopy or magnetic resonance spectroscopy (MRS), is a spectroscopic Spectroscopy is the study of the interaction between matter and Electromagnetism, electromagnetic ra ...
at low temperature (−78 °C) with support from
density functional theory Density-functional theory (DFT) is a computational quantum mechanical modelling method used in physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ''phýsis'' 'nature'), , is ...
computation. These oxonium ions were also demonstrated to directly give rise to multiple related
natural product A natural product is a chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entity, molecular entities) composed of atoms from more than one chemical element, element held together b ...
s by reacting with various
nucleophile In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, behavior and the changes they undergo during a ...

nucleophile
s, such as water, bromide, chloride and acetate.


See also

*
Onium ion An “-onium” (plural: onia) is a bound state In quantum physics Quantum mechanics is a fundamental theory in physics that provides a description of the physical properties of nature at the scale of atoms and subatomic particles. It is the ...
, a +1 cation derived by protonation of a hydride (includes oxonium ions) *
Pyrylium Pyrylium is a cation An ion () is a particle, atom or molecule with a net electric charge, electrical charge. The charge of the electron is considered negative by convention. The negative charge of an ion is equal and opposite to charged p ...

Pyrylium
, another type of ion with +1 formal charge on oxygen *
Sulfonium A sulfonium ion, also known as sulphonium ion or sulfanium ion, is a positively charged ion (a "cation") featuring three organic Substitution (chemistry), substituents attached to sulfur. These organosulfur compounds have the formula . Toget ...
, a heavier congener


References

{{Reflist Oxycations Oxonium compounds